The present invention relates to a cleaning device for a fixing unit capable of fixing an image produced for example by an electric photocopier or the like on a support essentially formed by a fuser assembly, in contact with which there moves a film that is rolled up in a ring configuration to form an endless belt which is set in motion by an entrainment roller which transmits a drive torque to the film by means of the friction between its external surface and the internal surface of the film with which it is in contact, and more particularly a cleaning device capable of removing contaminating particles from the external surface of the drive roller, keeping it clean for the purposes of maintaining constant in respect of time the coefficient of friction as between the film and the entrainment roller.
A fixing unit is known in the current state of the art, which is formed by:
a fuser assembly comprising a support of heat-resistant resin, and a heating element fixed to the support and formed by an alumina base on which a resistance means is deposited using the thick-film technology; PA1 a film of heat-resistant material which is rolled up in a ring configuration to form an endless belt, which moves in contact with the heating element and which is wrapped around two rotatable rollers of which one constitutes the entrainment roller and the other, which rotates idly, constitutes a tensioning roller; and PA1 a pressure roller which applies a pressure between the support on which the image to be fixed is formed and the fuser assembly, by way of the film.
The drive roller transmits a drive torque to the belt to make it move, by means of the frictional force between its external surface and the internal surface of the belt with which it is in contact; that frictional force depends on the tension of the belt, the angle through which it is wrapped around the drive roller and the coefficient of friction between the two materials constituting the external surface of the drive roller and the internal surface of the belt.
The movement of the film is opposed substantially by a resistant torque generated by the frictional force between the internal surface of the belt and the external surface of the heating element. Various systems are known in the current state of the art for reducing the latter frictional force and to keep it low for as long as possible, for example by depositing a layer of amorphous carbon like diamond on the external surface of the heating element, as described in Italian patent application No TO93A000952.
However those arrangements are not sufficient to guarantee that the fixing unit enjoys a long service life; in fact, with use, the abrasion effect caused by the belt rubbing against the fuser group generates minute particles of the materials which make up the surfaces that are in contact, which particles, being transported by the belt, are deposited and accumulate on the external surface of the drive roller, with the effect of reducing the coefficient of friction between the external surface of the drive roller and the internal surface of the belt, finally causing the belt to slip with respect to the drive roller and resulting in it consequently coming to a stop.